2. Field of the Invention
The invention relates to a method of applying a combination of cellulolytic enzymes with cationic and anionic polymers for use in enhancing the freeness of pulp a in papermaking process and, more particularly, a multiple feed point process for the use of the cellulolytic enzymes.
3. Description of the Prior Art
Use of cellulolytic enzymes, e.g. cellulases and/or the hemicellulases for treating recycled paper pulps to improve freeness is the subject of U.S. Pat. No. 4,923,565 the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 5,169,497, issued to Sarkar and Cosper discusses the effects of cellulases in combination with cationic flocculants of varying composition on the freeness of old corrugated containers (OCC) pulp. The '497 patent covers the use of a combination of enzyme and cationic polymers for enhancing the freeness of recycled fiber. In practice, dual polymer treatment programs are also used for retention.
In a dual polymer retention system, two synthetic polymers are mixed with the pulp sequentially to achieve better results than obtained with either polymer by itself. These improved results are specifically aimed at increasing the retention of pulp fibers on the paper sheet. Increased retention results in a paper sheet having increased strength.
Usually, a low molecular weight, highly charged cationic polymer is added to the papermaking process first and, at a later stage, a high molecular weight, anionic polymer is added. Good retention has numerous economic benefits. As the use of recycled fiber increases in container board, fine paper, and newsprint grades, the opportunity to provide benefits through retention aids has also increased. If fines are not retained by a good retention aid or hydrolyzed by an enzyme, they will impede drainage, fill felts, and cause deposition problems. The key benefit of retention aids with enzyme is to prevent drainage reduction and subsequent loss of machine speed. Drainage can be maintained by preventing the build-up of fines in the white water loop.
U.S. Pat. No. 5,308,449, issued to Fuentes et al. discusses the use of enzymes as a method of treating recycled paper for use as a papermaking pulp. There is no discussion in Fuentes et al. of the use of treatment agents for enhancing the freeness and drainability of pulp once the recycled paper has been introduced back into the papermaking process.
Ideally, a method would exist which would increase the freeness of paper pulp while at the same time maintaining the strength necessary to produce a defect-free paper sheet.